CVE-2020-37167: ClamAV Bytecode Interpreter RCE Vulnerability

CVE-2020-37167 Overview

CVE-2020-37167 is a Code Injection vulnerability affecting the ClamAV ClamBC bytecode interpreter. The vulnerability exists in the function name processing component, which allows attackers to manipulate bytecode function names due to weak input validation in function name encoding. This flaw can potentially be exploited to execute malicious bytecode or cause unexpected behavior in the ClamAV engine.

Critical Impact
Attackers with local access can exploit weak input validation in the ClamBC bytecode interpreter to potentially execute malicious bytecode, leading to high impact on confidentiality, integrity, and availability of the affected system.

Affected Products

ClamAV ClamBC Bytecode Interpreter (versions not specified)

Discovery Timeline

2026-02-12 - CVE CVE-2020-37167 published to NVD
2026-02-12 - Last updated in NVD database

Technical Details for CVE-2020-37167

Vulnerability Analysis

This vulnerability is classified under CWE-94 (Improper Control of Generation of Code - Code Injection). The ClamAV ClamBC bytecode interpreter processes function names without adequate input validation, creating an attack surface for code injection attacks.

The vulnerability resides in the bytecode interpreter's handling of function names during bytecode processing. When the interpreter parses and processes bytecode files, it fails to properly validate and sanitize function name encodings. This weakness allows specially crafted bytecode to bypass security controls and potentially execute arbitrary code within the context of the ClamAV engine.

Given the local attack vector, an attacker would need to have the ability to supply malicious bytecode files to the ClamAV scanner. This could occur in scenarios where ClamAV processes user-uploaded files, scans shared directories, or processes files from untrusted sources.

Root Cause

The root cause of this vulnerability is improper input validation in the function name encoding mechanism within the ClamBC bytecode interpreter. The interpreter does not adequately verify that function names conform to expected formats and constraints, allowing malformed or malicious function name data to be processed. This lack of strict validation creates an opportunity for attackers to inject code through specially crafted bytecode function names.

Attack Vector

The attack vector for CVE-2020-37167 is local, meaning an attacker must have the ability to submit bytecode files to the ClamAV engine for processing. Exploitation involves crafting a malicious bytecode file with manipulated function names that exploit the weak validation logic in the interpreter.

Attack scenarios include:

Uploading malicious files to systems where ClamAV performs automatic scanning
Placing crafted bytecode files in directories monitored by ClamAV
Exploiting mail gateways or web applications that use ClamAV for file scanning

The vulnerability mechanism involves crafting bytecode with specially encoded function names that bypass validation checks in the ClamBC interpreter. For detailed technical information, refer to the VulnCheck Security Advisory and Exploit-DB #47687.

Detection Methods for CVE-2020-37167

Indicators of Compromise

Unusual bytecode files with anomalous function name patterns being processed by ClamAV
Unexpected behavior or crashes in the ClamAV daemon (clamd) during file scanning operations
Suspicious file activity in ClamAV scan directories or quarantine locations
Abnormal memory usage or CPU consumption by ClamAV processes

Detection Strategies

Monitor ClamAV logs for parsing errors, crashes, or unusual bytecode processing failures
Implement file integrity monitoring on ClamAV configuration and bytecode signature files
Deploy endpoint detection solutions capable of identifying exploitation attempts targeting antivirus engines
Use SentinelOne's behavioral AI to detect anomalous process behavior from ClamAV components

Monitoring Recommendations

Enable verbose logging in ClamAV to capture detailed information about bytecode processing
Set up alerts for ClamAV service crashes or unexpected restarts
Monitor for unusual file types or patterns being submitted to ClamAV scanners
Implement network monitoring for systems where ClamAV processes files from external sources

How to Mitigate CVE-2020-37167

Immediate Actions Required

Update ClamAV to the latest available version that addresses this vulnerability
Review and restrict which file types are processed by ClamAV bytecode scanning
Limit access to systems where ClamAV processes untrusted files
Consider temporarily disabling bytecode scanning if immediate patching is not possible

Patch Information

Consult the ClamAV Official Website for the latest security updates and patched versions. Review the VulnCheck Security Advisory for specific remediation guidance related to this vulnerability.

Organizations should prioritize updating ClamAV installations, particularly on systems that process files from untrusted sources such as mail gateways, web application servers, and file sharing platforms.

Workarounds

Disable ClamAV bytecode scanning feature if not required for operations using the Bytecode configuration directive
Implement strict file filtering before files reach ClamAV to reduce exposure to malicious bytecode
Run ClamAV in a sandboxed or containerized environment to limit potential impact from exploitation
Apply network segmentation to isolate systems running ClamAV from critical infrastructure

bash

# Configuration example - Disable bytecode scanning in clamd.conf
# Add or modify the following line in your ClamAV configuration
echo "Bytecode no" >> /etc/clamav/clamd.conf
# Restart the ClamAV daemon to apply changes
systemctl restart clamav-daemon